A summary of python code style conventions

As I've just started to learn python, I should make an effort to internalise these best-practice conventions. To help me do that, I'm going to summarise PEP 8 and 257 here, as a quick reference for myself and anyone else who might find it useful.

This is not quite an exhaustive summary: I have omitted the really obvious stuff, and in some cases I've picked one approach where PEP8 allows a few.